Regulation of calcium and phosphate balance
- Jonathan Hogan, MD
Jonathan Hogan, MD
- Assistant Professor of Medicine
- Perelman School of Medicine at the University of Pennsylvania
- Stanley Goldfarb, MD
Stanley Goldfarb, MD
- Editor-in-Chief — Nephrology
- Section Editor — Mineral and Bone Metabolism; Renal Ureteral Stones
- Professor of Medicine
- University of Pennsylvania School of Medicine
The maintenance of calcium and phosphate homeostasis involves intestinal, bone, and renal handling of these ions.
Within the plasma, calcium circulates in different forms. Of the plasma calcium, roughly 40 percent is bound to albumin, 15 percent is complexed with citrate, sulfate, or phosphate, and 45 percent exists as the physiologically important ionized (or free) calcium. As routinely measured in the laboratory, the plasma calcium concentration includes all of the calcium in the plasma (free and bound). In general, measuring the total plasma calcium concentration is sufficient since changes in this parameter are usually associated with parallel changes in the ionized concentration. Exceptions to this commonly occur in patients with hypoalbuminemia, acid-base disorders, and chronic kidney disease. Issues surrounding the measurement of total and ionized calcium are presented elsewhere in detail. (See "Relation between total and ionized serum calcium concentrations".)
In comparison to calcium, plasma phosphorus exists in both organic and inorganic forms, including phospholipids, ester phosphates, and inorganic phosphates. Inorganic phosphates are completely ionized, circulating primarily as HPO42- or H2PO4- in a ratio of 4:1 at a plasma pH of 7.40.
Only a small fraction of the total body calcium and phosphate is located in the plasma. However, it is the plasma concentrations of ionized calcium and inorganic phosphate that are under hormonal control. Calcium balance is mediated primarily by parathyroid hormone (PTH) and calcitriol (1,25-dihydroxyvitamin D), which affect intestinal absorption, bone formation and resorption, and urinary excretion [1-4]. Phosphorous balance is also primarily regulated by PTH but may also respond to fibroblast growth factor 23 (FGF-23) and its cofactor, Klotho, which together and separately promote renal excretion of phosphorous [5,6]. The physiologic roles of other hormones (such as calcitonin and estrogens) in the regulation of calcium and phosphate balance are incompletely understood .
Gastrointestinal calcium handling — Dietary calcium is absorbed by two mechanisms :To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information on subscription options, click below on the option that best describes you:
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- CALCIUM HANDLING
- Gastrointestinal calcium handling
- Bone calcium handling
- Renal calcium handling
- REGULATION OF PLASMA CALCIUM CONCENTRATIONS
- Parathyroid hormone
- Vitamin D
- - Effect of vitamin D on calcium
- - Regulation of vitamin D
- Direct effects of the plasma calcium
- PHOSPHATE HANDLING AND REGULATION
- Phosphate handling
- Regulation of plasma phosphate concentrations